On Wide-Angle Vehicular Distortion

A study on how wide-angle lenses affect vehicles proportions when photographed off-center.

Wide-angle distortion can be used for artistic effects but if the job to be done is to advertise a vehicle, the client is most likely looking for an undistorted view of the product, free from extreme perspective deformation, in order to better represent it to potential customers.

In this video that was previously linked to in the article about motion blur, automotive photographer Nigel Harniman briefly mentions using an Alpa and a 58mm lens on a Phase One back — which roughly corresponds to a 35mm lens on a full frame camera — as his choice of camera for the availability of movements to avoid distorting the car. This means placing the vehicle in the center of the image, then using rise and shift to compose the frame, essentially deforming the landscape instead of the car. The same technique can be applied in CG to provide more natural, less distorted vehicle renders.

Testing

The further away from the center of projection the more extreme the perspective of a 3D object becomes, and the wider the lens used the more pronounced the effect. The following test attempts to visually quantify this by keeping a consistent frame while moving the camera closer or further as necessary to a test field of spheres. For fun, I’m calling these Nico’s Indicatrix™.

The testing setup: the camera moves closer to the subject as the focal length diminishes to keep the framing consistent.

It’s important to note that the test subject, in this case simple spheres, needs to be in 3 dimensions, because the distortion only happens in the distance axis, and not on a plane parallel to the camera. If using flat circles instead of spheres in the above setup, no distortion would be visible because of the lack of depth relative to the camera plane.

As can be seen in the following plates, distortion away from the center of projection clearly becomes more noticeable for geometric objects near the edges of the frame below a focal length of 35mm on a full frame camera:

The problem can be clearly demonstrated for automotive renders by taking a 21mm lens — not uncommon for landscape work — as an extreme example:

Center and edge framing of an automotive subject. The camera is rotated around the entrance pupil to avoid any parallax shift. Subject rendered in the center of the frame on the left, one the edge of the frame on the right. Car model by natman.

Conclusion

Since people are accustomed and sensitive to vehicular proportions, the deformation near the edges below 35mm on a full frame camera is objectionable. If the vehicle needs to be composited off-center on the backplate, the solution is to start by positioning it centered to avoid the corner perspective distortion of a wide-angle lens, and move it at the right location by using the virtual camera shift controls.

Technology has revolutionized photography, but the timelessness of composition is evident in that an old-world technique — view camera movements — is still very much relevant in the digital domain.